Approximately 40~50% of GBMs show amplification of EGFR with most expressing an activated mutant receptor (EGFRvIII) as a driving oncogene, associated with hyper-activation of STAT3. Nonetheless, EGFR inhibition has thus far met with clinical failure, mostly due to PTEN deficiency. The central theme of this RO1 grant application focuses on the molecular mechanism of how the newly identified small molecule G5- 7 selectively inhibits Jak2/EGFR/STAT3 axis and exerts the therapeutic efficacy toward this most malignant GBM. In our preliminary study, we have identified G5-7 via cell-based drug screening using U87MG/EGFRvIII to mimic the genetic alteration in GBM patients with EGFR amplification and PTEN deficiency, and found that this compound exhibits potent anti-GBM activity in an intracranial model. G5-7 binds to FERM domain of Jak2 and blocks EGFR and STAT3 phosphorylation, robustly inhibiting human GBM neurosphere progression. Conceivably, Jak2 might bind to both EGFR and EGFRvIII and allow EGFR to phosphorylate EGFRvIII and induce its nuclear translocation, resulting STAT3 phosphorylation. Our overall hypothesis is that G5-7 disrupts the JAK2/EGFR/EGFRvIII signalsomes, suppressing GBM progression. This grant contains three specific aims that examine the anti-cancer mechanisms by G5-7. This highly integrated effort builds on the important discoveries of this small compound that selectively targets the most malignant GBM that are refractory to all other current therapies. The knowledge from this study will shed light on how allosteric inhibition of Jak2 specifically blocks EGFR/STAT3 axis' signaling cascades. The novel concept that Jak2/EGFR/EGFRvIII plays an essential role in driving GBM progression will provide an innovative therapeutic target for screening new compounds for treating the most devastating brain tumors and other solid tumors.